The present invention relates to a refrigeration system for use in an air-conditioner and, more particularly, to a refrigerant circuit of the refrigeration system, provided with a gas injection passage.
Generally, a refrigerant circuit of a refrigeration system has a closed loop constituted by a compressor, a condenser, a first pressure reducer, a gas-liquid separator, a second pressure reducer and an evaporator. When this refrigeration system is used in an air-conditioner, a gas injection passage provides a communication between the upper side of the gas-liquid separator and an intermediate stage of the compressor to inject refrigerant gas into the refrigerant which is being compressed to, increases the cooling or heating power of the air-conditioner.
In operation, the refrigerant gas discharged under high pressure from the compressor is introduced into the condenser and is liquefied in the condenser by radiating the heat through a heat exchange with an external fluid such as air or water. The liquid refrigerant is then depressurized to an intermediate pressure through the first pressure reducer so that a part of the refrigerant is evaporated. The liquid and gaseous phases of the refrigerant are then introduced into the gas-liquid separator and are separated from each other. The liquid phase of the refrigerant is extracted from the bottom of the gas-liquid separator and is introduced through the second pressure reducer to the evaporator which is held at a predetermined reduced pressure. In the evaporator, this liquid phase is evaporated through heat absorption from the external fluid such as air or water to become gaseous refrigerant which, in turn, is sucked by the compressor.
On the other hand, the gaseous refrigerant separated in the gas-liquid separator and accumulated in the upper part of the latter is injected through the gas injection passage into the intermediate stage of the compressor to merge in the refrigerant gas which is being compressed, thereby enhancing the heating or cooling power of the air-conditioner. However, if the refrigerant gas separated in the gas-liquid separator is injected into the compressor independently of the load demand, the pressure and temperature of the refrigerant gas discharged from the compressor will be increased excessively to unfavorable decrease the efficiency of the refrigeration cycle. In addition, the reliability of the air conditioner is impaired due to excessive temperature rise of the compressor and the motor by which the compressor is driven.
To avoid this problem, Japanese Patent Publication No. 47296/1980 proposes providing a stop valve in the gas injection passage and to close the same when the air conditioner is overloaded. This system, however, suffers from the following problem. Namely, if the pressure-reducing resistance of the first and second pressure reducers is selected optimumly for the gas injection, the flow rate of the refrigerant gas through the first pressure reducer is decreased when the gas injection circuit is closed to suspend the gas injection, as compared with the case where the gas injection is conducted, so that the refrigerant encounters smaller resistance across the second pressure reducer to cause the undesirable phenomenon of liquid back. Consequently, the refrigerating power, as well as the efficiency of the refrigeration cycle, are undesirably lowered.
The optimum flow rate of the refrigerant when the gas injection is conducted is substantially equal to that obtained when the gas injection is not conducted. In the prior art mentioned above, when the air conditioner is operating in the cooling mode, the liquid refrigerant accumulated in the gas-liquid separator is evaporated and discharged from the gas-liquid separator because the latter is heated by ambient air when the gas injection passage is closed, so that the flow rate of the refrigerant is seemingly increased. In order to optimize the flow rate of the refrigerant through the refrigeration cycle, therefore, it is necessary to provide a receiver for storing surplus refrigerant.
Japanese Utility Model Laid-Open No. 68454/1982 proposes another refrigerant circuit having a gas injection passage, in which no stop valve is provided in the gas injection passage. When the gas injection is not needed, only a part of the refrigerant is allowed to pass through the gas-liquid separator, while the other part flows bypass the gas-liquid separator. In this system, since a part of the refrigerant is allowed to flow to the evaporator through the gas-liquid separator even when the gas injection is not needed, the problem is encountered due to the fact that the gas-separator does not store surplus refrigerant.
Accordingly, an object of the invention is to provide a refrigeration system having a refrigerant circuit which can be switched between a first mode in which a gas injection is conducted (referred to as "gas injection mode", hereinafter) and a second mode in which the gas injection is not conducted (referred to as "non-injection mode", hereinafter) and which permits a control for optimizing the flow rates of the refrigerant in both of the first and second modes.
Another object of the invention is to provide a refrigeration system having a refrigerant circuit which can avoid excessive rise of pressure and temperature of the refrigerant gas discharged from the compressor while avoid liquid back to the compressor when the gas injection is not conducted.
To these end, according to one aspect of the invention, there is provided a refrigeration system having a main refrigerant circuit including a compressor, a condenser, a first pressure reducer, a gas-liquid separator, a second pressure reducer and an evaporator connected in series to form a closed loop, and a gas injection passage providing a communication between the gaseous phase part of the gas-liquid separator and a compression chamber of the compressor. A stop valve means is disposed in the inlet and outlet pipes of the gas-liquidified separator for opening and closing the inlet and outlet pipes when the injection of the refrigerant to the compressor is conducted and when the injection is not conducted, respectively. A bypass passage directly connects the outlet pipe of the condenser to the inlet pipe of the evaporator to bypass the gas-liquid separator. The stop valve means is adapted to be controlled such that, when the gas injection to the compressor through the gas injection passage is not conducted, the refrigerant flows through the bypass passage by-passing the gas-liquid separator, while the gas-liquid separator functions as a receiver for adjusting the amount of refrigerant circulated in the main refrigerant circuit.
According to another aspect of the invention, a refrigeration system is provided which comprises a heat-pump type refrigerant circuit including a compressor, a four-way valve, an outdoor heat exchanger, a pressure reducer for heating connected in parallel to a first check valve, a gas-liquid separator, a pressure reducer for cooling connected in parallel to a second check valve and an indoor heat exchanger connected in series, with the four-way valve being adapted to be switched over to switch the connection between the heat exchangers and the inlet and outlet pipes of the compressor. A gas injection passage provides a communication between the gaseous phase part of the gas-liquid separator and a compression chamber of the compressor and the pressure reducer for heating is used as a second pressure reducer for heating while the pressure reducer for cooling is used as a second pressure reducer for cooling. A stop valve means is disposed in the inlet pipe to the gas-liquid separator for opening and closing the inlet pipe when the injection of a refrigerant to the compressor is conducted and when the injection is not conducted, respectively. When the heat-pump type refrigerant circuit operates for cooling, the outlet side of the outdoor heat exchanger is connected to the second pressure reducer for cooling, through the first check valve, a first pressure reducer for cooling, the stop valve means in the inlet pipe to gas-liquid separator, interior of the gas-liquid separator, bottom of the gas-liquid separator, and a third check valve, whereas, when the heat-pump type refrigerant circuit operates for heating, the outlet side of the indoor heat exchanger is connected to the second pressure reducer for heating, through the second check valve, a first pressure reducer for heating, the stop valve means in the inlet pipe to the gas-liquid separator, interior of the gas-liquid separator, bottom of the gas-liquid separator and a fourth check valve. When the heat-pump type refrigerant circuit operates for cooling without gas injection, the first pressure reducer for cooling and the second pressure reducer for cooling are connected by a bypass passage for cooling by-passing the gas-liquid separator, whereas, when the heatpump type refrigerant circuit operates for heating without gas injection, the first pressure reducer for heating and the second pressure reducer for heating are connected through a bypass passage for heating bypassing the gas-liquid separator; whereby, when the injection of the refrigerant is not conducted, the refrigerant flows through either of the bypass passage for cooling and the bypass passage for heating bypassing the gas-liquid separator, while the gas-liquid separator serves as a reservoir for adjusting the amount of the refrigerant circulated through the refrigerant circuit.
In the refrigerant circuit of the invention, the refrigerant flows through the bypass passage bypassing the gas-liquid separator when the gas injection is not conducted, and the gas-liquid separator functions as a receiver for storing surplus refrigerant.
More specifically, when the gas injection is not conducted, the pressure of the refrigerant is reduced to a predetermined level through three pressure reducers connected in series: namely, the first pressure reducer, the auxiliary pressure reducer and the second pressure reducer.
In the non-injection mode, the flow rate of the refrigerant flowing through the first pressure reducer is small as compared with that in the gas-injection mode. Consequently, in order to optimize the flow rate of the refrigerant, it is necessary to increase the flow resistance of the refrigerant circuit. According to the invention, when the gas injection is not conducted, the auxiliary pressure reducer of the bypass passage takes part in the refrigeration circuit to optimize the flow resistance in the refrigeration circuit as a whole. It is, therefore, possible to maintain a moderate degree of dryness of the refrigerant at the evaporator outlet.
In addition, since the flow rate of the refrigerant in the refrigeration cycle is substantially equal in both modes, it is necessary to store the liquid refrigerant in the gas-liquid separator even in the non-injection mode. According to the invention, as explained before, the liquid refrigerant is held in the gas-liquid separator when the gas injection is not conducted, partly because the pressure in the gas-liquid separator is lower than the pressure at the inlet side of the second pressure reducer and partly because the inlet and outlet sides of the gas-liquid separator are closed by the solenoid valve and the check valve. Thus, in the non-injection mode of the refrigerant circuit, the gas-liquid separator serves also as a receiver for adjusting the amount of the refrigerant.
Consequently, according to the invention, it becomes possible to control the capacity of the refrigeration cycle, while optimizing the flow rate of the refrigerant, as well as the degree of dryness at the evaporator outlet, regardless of whether the gas injection is conducted or not.
In addition, it becomes possible to avoid any reduction of the refrigerating (cooling) power and heating power, as well as excessive rise of the discharge pressure and temperature, while avoiding the liquid back to the compressor in the non-injection mode.